For health reasons the decaffeination of vegetable products has gained considerable significance. Moreover, the caffeine obtained as by-product can be profitably sold.
In several decaffeination processes the hydrolyzed coffee beans are decaffeinated by means of organic solvents. The recovery of the solvent is effected by distillation, for example, in the course of which the caffeine is obtained as by-product.
In order to avoid any contamination of the vegetable material by solvent residues, carbon dioxide has recently been used as extractant as it is unobjectionable under the health aspect (German Pat. Nos. 2,005,293 and 2,212,281). The carbon dioxide solvent in these processes is freed from dissolved caffeine by means of activated carbon.
Prior to re-use of spent activated carbon the adsorbed substances are normally pyrolyzed and thereafter the carbon is thermally reactivated. On account of the usefulness of caffeine such a method is uneconomical.
Therefore, efforts have been made to recover the adsorbed caffeine. In the selection of measures for desorption of caffeine it must be borne in mind that active carbon is a very good adsorbent, a circumstance which renders desorption difficult. Moreover, the use of any agent objectionable under the health aspect is to be avoided since the extraction was carried out with carbon dioxide for the very reason to exclude such agents. For efficient and economical regeneration of the activated carbon the solvent should have a high dissolving capacity for the adsorbed substance and good transporting properties for the substance; thereafter the mixture should be readily separable.
According to the teaching of German OS No. 2,544,116 the adsorbate is desorbed with supercritical gases, especially with carbon dioxide. Thereafter the dissolved adsorbate must be removed from the dissolving gas.
U.S. Pat. No. 4,298,736 describes a process in which caffeine adsorbed to activated carbon is desorbed with a food-grade liquid solvent which may be an organic acid or an alcohol. The process is preferably carried out above 100.degree. C. with glacial acetic acid or with azeotropic mixtures of glacial acetic acid and second components.
After regeneration of the activated carbon with non-volatile solvents the solvent must be separated from the activated carbon in any event with steam, for example. This necessarily calls for an additional step.
It is the problem underlying the invention to provide a simple and economical process for recovering caffeine adsorbed to activated carbon with simultaneous regeneration of the activated carbon; the desorption of caffeine from the activated carbon is to be effected with a food-grade agent.